REVISITING CARBONATE PRODUCTIVITY RATES OF HALIMEDA IN GRAHAM'S HARBOUR, SAN SALVADOR, BAHAMAS: DOES A 9 YEAR HIATUS IN SAMPLING SHOW A RESPONSE TO INCREASED ATMOSPHERIC CO2 LEVELS?

Calcareous green algae (Halimeda sp., Penicillus sp., Udotea sp. and Rhipocephalus sp.) are major suppliers of carbonate sediments in tropical regions. An extensive study was undertaken in July 2000 and December 2001 in Graham’s Harbour on San Salvador, Bahamas to quantify the amount of sediment produced by Halimeda and to establish the community structure and species richness and diversity of these algae (Freile, 2004 and Freile et al., 2005). In May 2009, 3 transects were run in Graham’s Harbour and compared to the 2000-2001 data. The coverage of the previous work was extensive (180 quadrats counted for diversity vs. 31 in 2009) and 110 specimens counted for growth in 2009 versus several hundred in 2000-2001. In addition, the short time spent in San Salvador in May 2009 (2 weeks versus a month in July 2000) also meant a shorter time for the in situ growth experiment. However, preliminary indications show that a turnover rate for an algal thallus is achieved at 35 days versus 47 days for the 2000-2001 time-frames. This means that there are 10.4 algal crops/yr in 2009 vs. 7.8 algal crops/yr in 2000-2001. Also the average segments per upright or rhipsalian alga (Halimeda) is 202 vs. 59 segments for the 2000-2001 data. Additionally, there appears to be slightly more algae per square meter 35 (2009) vs. 28 (2000-2001) than before. These data would at first glance indicate a higher photosynthetic activity on the part of the algae, but more work needs to be conducted to verify these results. To date, we have not detected any change at the community level. Community indices (e.g. species richness- the assemblage of algae Halimeda sp., Penicillus sp., Udotea sp. and Rhipocephalus sp.) have remained unchanged since 2000-2001 (Freile et al., 2005). This may be due to the fact that the community is not impacted; or, it could be due to the fact that we lack a long term set of data for both community structure and productivity. Future monitoring and studies will be invaluable in elucidating the relationships, if any, that exist between productivity and community structure in response to elevated levels of CO₂.